Coagulation is a physiochemical operation used in water treatment. The process causes the destabilization and aggregation of smaller particles into larger particles. Generally, water contaminants such as ions (heavy metal) and colloids (organics and inorganics) are suspended in solution by electrical charges. Colloidal contaminants can be destabilized by the addition of ions having a charge opposite to that of the colloidal contaminant. The destabilized colloids can be aggregated and subsequently removed by sedimentation and/or filtration.
Coagulation can be achieved by chemical or electrical means. Electrocoagulation is an electro-chemical process that simultaneously removes heavy metals, suspended solids, emulsified organics and many other contaminants from water by passing electric current through the water. The process uses DC current, consumable anodes and cathodes to combine with contaminants in a waste stream, thus producing insoluble oxides and hydroxides, called floc, that are easily separated from the clear water. A variety of anode and cathode geometries, including plates, balls, fluidized bed spheres, wire mesh, rods and tubes have been utilized for the process.
In a common prior art system, contaminated water passes in a layer between metal plates charged with a direct electrical current. The plate material is discharged, as molecules, into the stream, where ionic and non-ionic contaminants are subjected to the electrical charge, electrolysis products, and the plate elements. The process produces a number of effects depending on the species present, but generally contaminants are reacted to their most stable state as floc, and then are removed from the wastewater by physical means—typical solids separation methods like clarification, settling tanks or weir plates may be employed.
It is known in the art that EC suffers from several shortcomings that limit the utility of the method. In a typical EC system, the spacing between the plates is commonly small (less than 1 inch) with many plates inside a unit. This limits the volumetric flow rate and requires very large units or a large number of smaller units. The buildup of corrosion byproducts will often create a bridge or “short” in the system and therefore these systems require constant maintenance and cleaning. Lastly, the pathway through the EC unit does not always provide adequate contact with the water being treated because of lack of mixing.
Accordingly, in view of the foregoing shortcomings, there is a need in the art for a system and process that overcomes the current limitations by providing excellent contact with the charged plates, thorough mixing, and no cleaning requirement, as well as possessing the ability to be taken out of service for extended periods and put back into service without protracted time limitations.